In an internal gear pump (trochoid pump), an inner rotor and an outer rotor having a trochoid tooth profile are hermetically sealed in a casing. The outer rotor and inner rotor, which is fixed to a drive shaft, rotate along with the rotation of the drive shaft and act to suction and discharge liquids. Examples of this type of pump are submitted, e.g., in patent documents 1 to 3.
An example of a conventional internal gear pump is shown in FIGS. 11 and 12. FIG. 11 is a perspective view of the assembly of a conventional internal gear pump. FIG. 12(a) is a sectional view of the internal gear pump of FIG. 11, and FIG. 12(b) is a sectional view of an internal gear pump having a different configuration. As shown in FIG. 11, the pump 21 mainly comprises a trochoid 24 in which an inner rotor 23 having a plurality of outer teeth is accommodated inside an annular outer rotor 22 having a plurality of inner teeth. The trochoid 24 is rotatably accommodated in a circular trochoid-accommodating recess 25a formed in a flanged, cylindrical casing 25. A cover 26 for closing off the trochoid-accommodating recess 25a is fixed on the casing 25. As shown in FIG. 12(a), the casing 25 and the cover 26 are securely fixed by bolts 30 on a fixing plate 28 of the device body. The mating faces of the casing 25 and the cover 26 are machined faces that are face-sealed.
The trochoid 24 is configured so that the outer teeth of the inner rotor 23 mesh with the inner teeth of the outer rotor 22 and the inner rotor 23 is rotatably accommodated inside the outer rotor 22 in an eccentric state. Suction-side and discharge-side chambers are formed in accordance with the rotating direction of the trochoid 24 between partitioning points where the rotors are in contact with each other. A drive shaft 31 (not shown in FIG. 11) that is made to rotate by a drive source such as a motor (not shown) passes through, and is fixed, in the axial center of the inner rotor 23. A bearing 32 for supporting the drive shaft 31 is press-fitted into the cover 26. When the drive shaft 31 rotates and the inner rotor 23 rotates, the outer rotor 22 rotates in turn in the same direction as a result of the outer teeth of the inner rotor 23 meshing with the inner teeth of the outer rotor 22. Liquid is suctioned from an inlet into the suction-side chamber, which increases in volume and drops to negative pressure, by the rotation of the rotors. This suction-side chamber undergoes a decrease in volume and an increase in internal pressure due to rotation of the trochoid 24 and is converted to a discharge-side chamber. The suctioned liquid is then discharged to an outlet.
The bearing 32 can be a roller bearing, or a plain bearing such as a metal bush (an alloy of copper, tin, lead, or the like) or a bush wrapped with a polytetrafluoroethylene (abbreviated as PTFE below) resin. Of these examples, an inexpensive plain bearing is often used. When a plain bearing is to be press-fitted into the cover 26, a bearing press-fitting part of the cover 26 is finished by machining before the press-fitting. Furthermore, the inside diameter of the plain bearing is machined after press-fitting in order to manage the clearance to the drive shaft 31.
A liquid-suctioning nozzle 27 that extends from the casing 25 is provided as necessary on the inlet that communicates with the suction-side chamber (FIG. 12(b)). A metallic or resinous mesh filter 29 for removing foreign matter in the suctioned liquid is installed at a desired location in the inlet pathway leading to the suction-side chamber, including the nozzle 27. The mesh filter 29 is spot-welded or physically fixed with a C-ring, etc. The mesh filter 29 or the liquid-suctioning nozzle 27 is installed with a rubber packing, interposed to ensure sealing performance.